feat(datafusion-spark): implement spark compatible unhex function (#19909)

## Which issue does this PR close?

<!--
We generally require a GitHub issue to be filed for all bug fixes and
enhancements and this helps us generate change logs for our releases.
You can link an issue to this PR using the GitHub syntax. For example
`Closes #123` indicates that this PR will close issue #123.
-->

Part of: #15914

## Rationale for this change

<!--
Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
Explaining clearly why changes are proposed helps reviewers understand
your changes and offer better suggestions for fixes.
-->

Implement spark compatible unhex functions:
https://spark.apache.org/docs/latest/api/sql/index.html#unhex

## What changes are included in this PR?

<!--
There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
-->

## Are these changes tested?
Yes. UTs and SLT added.

<!--
We typically require tests for all PRs in order to:
1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code

If tests are not included in your PR, please explain why (for example,
are they covered by existing tests)?
-->

## Are there any user-facing changes?
No.

<!--
If there are user-facing changes then we may require documentation to be
updated before approving the PR.
-->

<!--
If there are any breaking changes to public APIs, please add the `api
change` label.
-->

Author: lyne7-sc

datafusion/spark/Cargo.toml

@@ -79,3 +79,7 @@ name = "slice"
 [[bench]]
 harness = false
 name = "substring"
+
+[[bench]]
+harness = false
+name = "unhex"

datafusion/spark/benches/unhex.rs

@@ -0,0 +1,148 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+extern crate criterion;
+
+use arrow::array::{
+    Array, LargeStringArray, LargeStringBuilder, StringArray, StringBuilder,
+    StringViewArray, StringViewBuilder,
+};
+use arrow::datatypes::{DataType, Field};
+use criterion::{Criterion, criterion_group, criterion_main};
+use datafusion_common::config::ConfigOptions;
+use datafusion_expr::{ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl};
+use datafusion_spark::function::math::unhex::SparkUnhex;
+use rand::rngs::StdRng;
+use rand::{Rng, SeedableRng};
+use std::hint::black_box;
+use std::sync::Arc;
+
+fn generate_hex_string_data(size: usize, null_density: f32) -> StringArray {
+    let mut rng = StdRng::seed_from_u64(42);
+    let mut builder = StringBuilder::with_capacity(size, 0);
+    let hex_chars = b"0123456789abcdefABCDEF";
+
+    for _ in 0..size {
+        if rng.random::<f32>() < null_density {
+            builder.append_null();
+        } else {
+            let len = rng.random_range::<usize, _>(2..=100);
+            let s: String = std::iter::repeat_with(|| {
+                hex_chars[rng.random_range(0..hex_chars.len())] as char
+            })
+            .take(len)
+            .collect();
+            builder.append_value(&s);
+        }
+    }
+    builder.finish()
+}
+
+fn generate_hex_large_string_data(size: usize, null_density: f32) -> LargeStringArray {
+    let mut rng = StdRng::seed_from_u64(42);
+    let mut builder = LargeStringBuilder::with_capacity(size, 0);
+    let hex_chars = b"0123456789abcdefABCDEF";
+
+    for _ in 0..size {
+        if rng.random::<f32>() < null_density {
+            builder.append_null();
+        } else {
+            let len = rng.random_range::<usize, _>(2..=100);
+            let s: String = std::iter::repeat_with(|| {
+                hex_chars[rng.random_range(0..hex_chars.len())] as char
+            })
+            .take(len)
+            .collect();
+            builder.append_value(&s);
+        }
+    }
+    builder.finish()
+}
+
+fn generate_hex_utf8view_data(size: usize, null_density: f32) -> StringViewArray {
+    let mut rng = StdRng::seed_from_u64(42);
+    let mut builder = StringViewBuilder::with_capacity(size);
+    let hex_chars = b"0123456789abcdefABCDEF";
+
+    for _ in 0..size {
+        if rng.random::<f32>() < null_density {
+            builder.append_null();
+        } else {
+            let len = rng.random_range::<usize, _>(2..=100);
+            let s: String = std::iter::repeat_with(|| {
+                hex_chars[rng.random_range(0..hex_chars.len())] as char
+            })
+            .take(len)
+            .collect();
+            builder.append_value(&s);
+        }
+    }
+    builder.finish()
+}
+
+fn run_benchmark(c: &mut Criterion, name: &str, size: usize, array: Arc<dyn Array>) {
+    let unhex_func = SparkUnhex::new();
+    let args = vec![ColumnarValue::Array(array)];
+    let arg_fields: Vec<_> = args
+        .iter()
+        .enumerate()
+        .map(|(idx, arg)| Field::new(format!("arg_{idx}"), arg.data_type(), true).into())
+        .collect();
+    let config_options = Arc::new(ConfigOptions::default());
+
+    c.bench_function(&format!("{name}/size={size}"), |b| {
+        b.iter(|| {
+            black_box(
+                unhex_func
+                    .invoke_with_args(ScalarFunctionArgs {
+                        args: args.clone(),
+                        arg_fields: arg_fields.clone(),
+                        number_rows: size,
+                        return_field: Arc::new(Field::new("f", DataType::Binary, true)),
+                        config_options: Arc::clone(&config_options),
+                    })
+                    .unwrap(),
+            )
+        })
+    });
+}
+
+fn criterion_benchmark(c: &mut Criterion) {
+    let sizes = vec![1024, 4096, 8192];
+    let null_density = 0.1;
+
+    // Benchmark with hex string
+    for &size in &sizes {
+        let data = generate_hex_string_data(size, null_density);
+        run_benchmark(c, "unhex_utf8", size, Arc::new(data));
+    }
+
+    // Benchmark with hex large string
+    for &size in &sizes {
+        let data = generate_hex_large_string_data(size, null_density);
+        run_benchmark(c, "unhex_large_utf8", size, Arc::new(data));
+    }
+
+    // Benchmark with hex Utf8View
+    for &size in &sizes {
+        let data = generate_hex_utf8view_data(size, null_density);
+        run_benchmark(c, "unhex_utf8view", size, Arc::new(data));
+    }
+}
+
+criterion_group!(benches, criterion_benchmark);
+criterion_main!(benches);

datafusion/spark/src/function/math/mod.rs

@@ -22,6 +22,7 @@ pub mod hex;
 pub mod modulus;
 pub mod rint;
 pub mod trigonometry;
+pub mod unhex;
 pub mod width_bucket;
 
 use datafusion_expr::ScalarUDF;
@@ -35,6 +36,7 @@ make_udf_function!(hex::SparkHex, hex);
 make_udf_function!(modulus::SparkMod, modulus);
 make_udf_function!(modulus::SparkPmod, pmod);
 make_udf_function!(rint::SparkRint, rint);
+make_udf_function!(unhex::SparkUnhex, unhex);
 make_udf_function!(width_bucket::SparkWidthBucket, width_bucket);
 make_udf_function!(trigonometry::SparkCsc, csc);
 make_udf_function!(trigonometry::SparkSec, sec);
@@ -57,6 +59,7 @@ pub mod expr_fn {
         "Returns the double value that is closest in value to the argument and is equal to a mathematical integer.",
         arg1
     ));
+    export_functions!((unhex, "Converts hexadecimal string to binary.", arg1));
     export_functions!((width_bucket, "Returns the bucket number into which the value of this expression would fall after being evaluated.", arg1 arg2 arg3 arg4));
     export_functions!((csc, "Returns the cosecant of expr.", arg1));
     export_functions!((sec, "Returns the secant of expr.", arg1));
@@ -71,6 +74,7 @@ pub fn functions() -> Vec<Arc<ScalarUDF>> {
         modulus(),
         pmod(),
         rint(),
+        unhex(),
         width_bucket(),
         csc(),
         sec(),